This invention relates to an improved hydraulic pump that is able to limit the amount of torque produced within the pump. More specifically and without limitation, this invention relates to a torque limiting system within a hydraulic piston pump.
The pressure compensated hydraulic piston pump is widely used in industry as a means of driving a wide range of hydraulic devices. The pressure compensated pump delivers a fixed maximum volume of fluid at pressures below the design level and then an abrupt cutoff of the flow as the design pressure level is reached. Such pumps are usually equipped with a variable pressure control which allows the cutoff pressure to be easily adjusted. The operation of the pump can be ascribed as follows: the pump is driven by an external power source through a shaft. A cylinder block is connected to and rotates with the shaft. A series of pistons in the cylinder block rotate with the block and rests against the side of a tilted swashplate which is located within the pump housing.
As the cylinder block rotates the pistons move back and forth in the block with their displacement controlled by the angled swashplate to the axis of the driveshaft. Valve orifices allow entry of fluid into the pump on the backstroke of the pistons and out of the pump on the forward stroke of the pistons. The inlet and outlet to the pump are located in an end cap. At a fixed rotational speed and fixed swashplate angle the pump will deliver a constant flow of fluid at varying pressures. A pressure compensating valve senses the hydraulic system pressure and as the pressure approaches the maximum operating pressure selected, opens a pressure compensating conduit to allow a flow of fluid under pressure. The pressure from the conduit then causes movement of a piston, thus causing movement of the swashplate.
Despite these advances in the art, a problem occurs when there is a need for a torque limitation upon the shaft used to drive the piston pump. Traditional torque control requires a displacement feedback in order to regulate pressure to achieve a constant torque curve. Hence, when the need of the hydraulic piston pump is only to clip the maximum input torque this displacement feedback is not required. Thus, there is a need in the art to provide for a torque control that is able to clip the maximum input torque without displacement feedback.
Attempts in the art have been made to solve this problem. For instance, in Cowan (U.S. Pat. No. 4,723,892), a helical spring is used in combination with altering the compensation and system pressures in order to control the piston pump. This system has many disadvantages including the use of a helical spring (which may be very large to achieve the desired effect) that requires additional mechanical parts and also results in compensator pressure working against the system pressure causing inefficiencies. Thus, there is a need in the art to provide a torque control that is able to limit the torque on a shaft that overcomes the stated problems.
Therefore, it is a principal object of the present invention to provide a torque control for a hydrostatic piston pump that will clip the maximum input torque of the piston pump without displacement feedback that improves upon the state of the art.
Yet another object of the present invention is to provide a torque control for a hydrostatic piston pump that does not use a helical spring element to control the maximum torque output of the hydrostatic cylinder piston pump.
Another object of the present invention is to provide a torque control for a hydrostatic piston pump that allows for compensator pressure and system pressure to act in the same direction to facilitate the control of the torque limiting control for a hydrostatic piston pump.
These and other objects, features, or advantages of the present invention will become apparent from the specification and claims.